The present invention relates to methods for sequentially laminated, rare earth, permanent magnets for use in high performance, rotating machines. The high electrical resistivity, rare earth, permanent magnets produced by the methods of the invention, with sulfide-based dielectric layers; are characterized by reduced eddy current losses combined with improved mechanical properties suitable for use in high performance, rotating machines. Rare earth, permanent magnets produced by methods of the present invention feature sulfide-based dielectric layer(s), combined with improved mechanical properties, are particularly well suited for commercial use in high performance, rotating machines, such as motors and generators.
Addressing eddy current losses in permanent magnets is critical in the design of high performance motors and high speed generators. Reduction of these eddy current losses in permanent magnets used with rotating machines is preferably accomplished by increasing the electrical resistivity of the permanent magnets. For example, when rare earth permanent, magnets are subjected to variable magnetic flux, and the electrical resistivity is low, excessive heat attributed to an eddy current is generated. This increased heat reduces the magnetic properties of the permanent magnet with corresponding reductions in the efficiency of rotating machines.
Adding layers of high resistivity, dielectric material to laminated, rare earth magnets, perpendicular to the plane of the eddy currents, generally results in a substantial decrease of eddy current losses. However, heretofore adding these layers of high resistivity material to laminated, permanent magnets were generally associated with shortcomings in mechanical properties. Specifically, these composite, laminated, permanent magnets with improved electrical resistivity failed in commercial use in high performance, rotating machines due to shortcomings in mechanical properties. Demands of high performance, rotating machines require improved mechanical properties beyond those traditionally available in laminates with suitable dielectric properties.
Rare earth, permanent magnets with improved electrical resistivity are described in U.S. Patent Publication No. US2006/0292395 A1 and U.S. Pat. Nos. 5,935,722; 7,488,395 B2; 5,300,317; 5,679,473; 5,763,085 and in U.S. patent application Ser. No. 12/707,227, filed Feb. 17, 2010, entitled “Rare Earth Laminated Composite Magnets with Increased Electrical Resistivity.
U.S. Patent Publication No. 2006/0292395 A1 teaches fabrication of rare earth magnets with high strength and high electrical resistance. The structure includes R—Fe—B-based rare earth magnet particles which are enclosed with a high strength and high electrical resistance composite layer consisting of a glass phase or R oxide particles dispersed in a glass phase, and R oxide particle based mixture layers (R=rare earth elements).
U.S. Pat. No. 5,935,722 teaches the fabrication of laminated composite structures of alternating metal powder layers, and layers formed of an inorganic bonding media consisting of ceramic, glass, and glass-ceramic layers which are sintered together. The ceramic, glass, and glass-ceramic layers serve as an electrical insulation material used to minimized eddy current losses, as well as an agent that bonds the metal powder layers into a dimensionally-stable body.
U.S. Pat. No. 7,488,395 teaches fabrication of a functionally graded rare earth permanent magnets having a reduced eddy current loss. The magnets are based on R—Fe—B (R=rare earth elements) and the method consists in immersing the sintered magnet body into a slurry of powders containing fluorine and at least one element E selected from alkaline earth metal elements and rare earth elements, mixed with ethanol.
Subsequent heat treatment of the magnets covered with the respective slurry allows for the absorption and infiltration of fluorine and element E from the surface into the body of the magnet. Thus, the magnet body includes a surface layer having a higher electric resistance than the interior.
U.S. patent application Ser. No. 12/707,227, (Pub. No. 2011-0200839) teaches laminated, composite, rare earth magnets with improved electrical resistivity.
To date, there is no teaching implied nor suggested in the prior art of the methods of the present invention which are responsible for producing:
A. “Intermediate” transition and/or diffusion reaction layers, combined with sequentially laminated layers of permanent magnets based on Sm—Co or Nd—Fe—B, where the transition and/or diffusion reaction layers surround and separate a sulfide-based, dielectric layer(s) from permanent magnet layers. The sequentially laminated, rare earth, permanent magnets of the present invention comprise Sm—Co or Nd—Fe—B layers separated from sulfide-based, dielectric layers by transition and/or diffusion reaction layers. All the layers in the sequentially laminated, rare earth, permanent magnet produced according to the methods of the present invention are consolidated simultaneously with the sequentially laminated, permanent magnet indicating acceptable magnetic properties with improved mechanical strength sufficient to support use with high performance, high speed rotating machines.B. Monolithic, sequentially laminated structures consisting of sequential layers of rare earth based magnets and layers of sulfide-based dielectric materials separated from the permanent magnet layers by transition and/or diffusion reaction layers. These sulfide-based, dielectric layers provide unexpected advantages in electrical resistivity as the laminated, dielectric layers partly interact at the interface, creating a transition and/or diffusion reaction layer separating the dielectric layer from the permanent magnet layer. The resultant sequentially laminated, rare earth, permanent magnets produced by the methods of the present invention exhibit exceptional electrical resistivity combined with no compromise in magnetic properties and improved mechanical strength.
There is no teaching in the prior art of manufacturing methods for producing “intermediate”, “transition”, and/or “diffusion reaction” layers separating laminated layers of rare earth, permanent magnet materials based on Sm—Co or Nd—Fe—B from layers of sulfide-based, dielectric materials selected from S or mixtures of sulfide and fluoride.
For purposes of the present invention, sulfide-based dielectrics include: Al2S3, Sb2S3, As2S3, BaS, BeS, Bi2S3, B2S3, CdS, CaS, CeS, Ce2S3, WS, Cr2S3, CoS, CoS2, Cu2S, CuS, Dy2S3, Er2S3, EuS, Gd2S3, Ga2S3, GeS, GeS2, HfS2, Ho2S3, In2S, InS, FeS, FeS2, La2S3, LaS2, La2O2S, PbS, Li2S, MgS, MnS, HgS, MoS2, Nd2S3, NiS, NdS, K2S, Pr2S3, Sm2S3, Sc2S3, SiS2, Ag2S, Na2S, SrS, Tb2S, Tl2S, ThS2, Tm2S3, SnS, SnS2, TiS2, WS2, US2, V2S3, Yb2S3, Y2S3, Y2S3, Y2O2S, ZnS and ZrS2 or a combination of any of these materials.
For purposes of the methods of manufacturing of the present invention, sulfide-based, dielectric materials include the sulfide compounds described above and:
Oxysulfides,
Sulfides and oxyfluorides,
Mixtures of sulfides,
Mixtures of sulfides and fluorides,
Mixtures of sulfides, fluorides, oxysulfides and/or oxyfluorides, and/or
Each of the above mixed with rare earth alloys.